1. Field of the Invention
The present invention relates to the field of foams for the suppression of hydrocarbon and polar organic vapors. More specifically, the present invention relates to aqueous foams for the suppression of hydrocarbon and polar organic vapors generated during loading of oil tankers, as well as during the transportation, transfer, storage, and accidental spillage of crude oil and lighter hydrocarbons.
2. Description of the Prior Art
During loading of oil tankers, and during the transportation, transfer, storage, and accidental spillage of crude oil and lighter hydrocarbons, a large quantity of vapors may be released which poses a fire hazard, as well as a threat to life or the environment. A vapor-recovery system can be used to remove the released hydrocarbon vapors, which vapors can then be incinerated later. This method, however, is expensive and ultimately releases carbon dioxide into the atmosphere.
Another possibility is suggested by U.S. Pat. No. 3,639,258 to Corino which involves the use of a gelling material to create an integral roof by gelling the upper layer of the oil in a tank to provide a floating roof of the same material. This technique, while useful for some purposes, creates considerable difficulties in cleaning and maintaining tanks or tanker compartments.
Alternatively, as suggested in U.S. Pat. No. 3,850,206 to Canevari et al. a foamed vapor barrier can be used to suppress the release of volatile hydrocarbons. The vast majority of conventional aqueous foams and foams for fire-fighting/vapor suppression, however, do not persist for more than 30 minutes and only a few persist for up to 2 hours. Accordingly, conventional aqueous foams do not persist for a sufficient time to allow their use in connection with the suppression of the release of hydrocarbon vapors during a lengthy procedure such as the loading of a tanker which takes from 16 to 20 hours. Adding to the foam solution a water thickener such as a polysaccharide, polyacrylamide or sulfonated polystyrene, as prescribed in Canevari et al. '206, extends the foam stability to no more than a few hours, especially when the temperature exceeds 90.degree. F.
In general, protein and fluoroprotein foams are capable of suppressing vapors of non-polar hydrocarbons below the lower explosive limit (LEL), usually about 2% or less of hydrocarbon gas in the air, for up to a few hours, but are not very effective against polar compounds.
Likewise, high-expansion foams of synthetic detergents and aqueous film-forming foams (AFFF), which form a spreading protective film over the hydrocarbon surface, are also capable of suppressing vapors of non-polar hydrocarbons for up to a few hours, but are equally ineffective against polar hydrocarbons.
Similarly, alcohol-type foams (ATF) consisting of a protein, surfactant, fluoroprotein or AFFF base and a metal stearate or polymer additive are capable of being effective for up to a few hours against polar hydrocarbons. In contrast, AFFF coupled with a polyurethane foam, e.g. the Light Water.RTM. ATC product sold by 3M, is very effective for longer suppression of polar and non-polar vapors. This product yields a semi-solid polyurethane foam with excellent mechanical strength. However, this type of foam leaves behind a non-collapsible polyurethane residue which is difficult to dispose of. Furthermore, all AFFF type foams contain a large amount of fluorocarbon surfactants which, although mostly inert, are not biodeqradable and must be disposed of in a landfill.
In any case, however, for most formulations, high-quality or high expansion foams having expansion ratios on the order of 100:1 to 1000:1 (100 to 1000 parts of gas for one part of foam solution) are the best types of foam for suppressing the release of volatile hydrocarbon vapors.
Three factors have been observed to control foam stability. In the first stage of foam life, water drainage controls foam stability. As water drains from the foam films (or lamellae), the films thin quickly to a small thickness. This stage usually lasts only a few minutes and is not very destructive to the bubbles. In the second stage of foam decay, the bubbles begin to slowly collapse, or coalesce into fewer but larger bubbles. Gas diffusion and, more importantly, water evaporation from the foam lamellae are the main causes of collapse at this stage. In the third and final stage, foam lamellae become so thin that small perturbations such as vibrations, shocks or sudden pressure or temperature changes, cause the remaining foam column to collapse catastrophically. All three stages of foam life usually last for less than a few hours. To further extend foam life, foam stability must be improved in all stages. Specifically, film drainage and water evaporation must be reduced, while mechanical strength must be improved.
In the presence of hydrocarbons, two additional factors further accelerate foam decay. First, hydrocarbon diffusion through the foam tends to destroy bubbles near the water-hydrocarbon interface. Second, surface active materials in the foam lamellae which are soluble in the hydrocarbons tend to partition into the hydrocarbons causing sudden collapse of the bubbles at the hydrocarbon interface.
The present invention overcomes the above-discussed disadvantages and drawbacks of the prior art. The present invention relates to new foam formulations with long stabilities in the presence of hydrocarbon and polar organic vapors. The formulations of the present invention include surface active materials and multi-functional additives which are selected to produce highly-stable foams, which will persist in the presence of hydrocarbon and polar organic vapors for several days at temperatures below 90.degree. F., and up to 24 hours at 105.degree. F. Unlike AFFF-polyurethane type foams, however, the formulations of the present invention leave behind only water-soluble residues, and a negliqible amount of fluorocarbons.